Tuned, or resonant, loads have been used in power electronics as a means of improving circuit efficiency and in reducing radiation at high frequencies. Switched power control elements are employed to apply energy to the loads and such elements will permit regulation of the power level. Regulation can be achieved by modulation of the power control stage supply voltage. Such voltage regulation is the best known and commonly employed method. However it requires expensive semiconductor power devices. Alternative methods of regulation can be achieved by the use of frequency modulation (FM) or pulse-width modulation (PWM) of the power control elements. However in most of the systems phase shift effects associated with off-resonance drives produce switching losses. Ideally if the switching devices are actuated at a zero current crossing such switching losses can be minimized but typically this only occurs for one set of control conditions.